Many electronic devices, such as smartphones, cellular phones, tablet and laptop computers, multimedia players, and e-book readers, include displays for displaying content to their respective users. Present-day displays are often constructed using liquid crystal display (LCD) panels and a light-emitting diode (LED) backlight. A front view of one such conventional electronic device 101 (e.g., a smartphone) is illustrated in FIG. 1. As illustrated, the electronic device 101 includes, among other things, a display 103 and a plurality of LEDs 105-109 (five shown for illustration) forming part of the display's backlight. When LED backlighting is used, the LEDs 105-109 are typically positioned within the electronic device 101 at one end of the display 103 and, upon being activated by the device's processing unit, illuminate the display 103 to present content 111 generated by the device's graphics processing unit (GPU).
FIG. 2 illustrates an exaggerated cross-sectional view of the display 103 along the line 2-2 of FIG. 1. As illustrated, the display 103 includes a printed circuit (PC) board 201, an LED backlight 203 positioned upon the PC board 201, and an LCD panel 205 positioned upon the LED backlight 203. The LED backlight 203 typically includes a reflection layer (reflector) 207 deposited on the PC board 201, a diffusion or light guide layer (light diffuser) 209 deposited upon the reflector 207, and a polarization layer (polarizer) 211 deposited upon the light diffuser 209. The LCD panel 205 is positioned upon and adhered to the polarizer 211. The LED backlight 203 also includes the LEDs 105-109 positioned at one end of the display 103 (in this example, the bottom end). When content is to be displayed on the display 103, the electronic device's processing unit activates the LEDs 105-109, which emit light into an end of the light diffuser 209. The emitted light propagates through the light diffuser 209 and is reflected toward the polarizer by the reflector 207. The reflected and diffused light is polarized by the polarizer 211 to illuminate the LCD panel 205. The illuminated LCD panel 205 then displays any content rendered therein by the device's GPU.
An exemplary display of digital clock content 111 on the electronic device's display 103 with the LEDs 105-109 illuminated is shown in FIG. 3. When the LEDs 105-109 are activated, they illuminate the entire display 103, even though the only content 111 being displayed is a digital clock positioned about one-quarter of the way down from the top of the display 103. Of course, other content, such as photos, icons, text, notifications, alerts, and other graphics, may be displayed at various locations of the display 103, as so desired. However, regardless of what amount of content is to be displayed, electronic device processing units are typically programmed or otherwise configured to activate all the LEDs 105-109 of an LED backlight 203 when displaying any content on the display 103.
Portable electronic devices that include LED backlit displays obtain power primarily from portable power sources, such as rechargeable batteries. Research has shown that displays, including LED backlit displays, consume a significant portion of a battery's power while they are activated. Thus, activating an LED backlit display to display a small amount of content, such as a digital clock, a small number of icons, a thumbnail photo, a notification, an alert, or any other small image, is an inefficient use of battery power. The desire to display only a small amount of content may arise where the electronic device 101 is configured to keep its display 103 always or almost always on, at least to a minor extent, or is awakened during sleep mode to provide a notification or alert to the device user.
To address the power consumption issue, there has been some discussion in the industry regarding independently controlling the LEDs 105-109 of an LED backlight, instead of activating/deactivating them all at once. However, due to the location of the LEDs 105-109 at one end of the display 103, a substantial portion of the display 103 would still be illuminated, and a significant amount of battery power used, even if only some of the LEDs 105-109 were activated to display a small amount of content. Additionally, turning on some, but not all, of the LEDs 105-109 of an LED backlight to display a small amount of content would produce undesirable artifacts across a substantial portion of the display 103.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated alone or relative to other elements or the elements may be shown in block diagram form to help improve the understanding of the various exemplary embodiments of the present invention.